Insights into oxidative stress in bone tissue and novel challenges for biomaterials

Strategies of functionalized GelMA-based bioinks for bone regeneration: Recent advances and future perspectives

Gelatin methacryloyl (GelMA) hydrogels is a widely used bioink because of its good biological properties and tunable physicochemical properties, which has been widely used in a variety of tissue engineering and tissue regeneration. However, pure GelMA is limited by the weak mechanical strength and the lack of continuous osteogenic induction environment, which is difficult to meet the needs of bone repair. Moreover, GelMA hydrogels are unable to respond to complex stimuli and therefore are unable to adapt to physiological and pathological microenvironments. This review focused on the functionalization strategies of GelMA hydrogel based bioinks for bone regeneration. The synthesis process of GelMA hydrogel was described in details, and various functional methods to meet the requirements of bone regeneration, including mechanical strength, porosity, vascularization, osteogenic differentiation, and immunoregulation for patient specific repair, etc. In addition, the response strategies of smart GelMA-based bioinks to external physical stimulation and internal pathological microenvironment stimulation, as well as the functionalization strategies of GelMA hydrogel to achieve both disease treatment and bone regeneration in the presence of various common diseases (such as inflammation, infection, tumor) are also briefly reviewed. Finally, we emphasized the current challenges and possible exploration directions of GelMA-based bioinks for bone regeneration.

Fullerol-reinforced antioxidantive 3D-printed bredigite scaffold for accelerating bone healing

Reactive oxygen species play a vital role in tissue repair, and nonequilibrium of redox homeostasis around bone defect can compromise osteogenesis. However, insufficient antioxidant capacity and weak osteogenic performance remain major obstacles for bone scaffold materials. Herein, integrating the mussel-inspired polydopamine (PDA) coating and 3D printing technologies, we utilized the merits of both osteogenic bredigite and antioxidative fullerol to construct 3D-printed porous, biodegradable acid-buffering, reactive oxygen species (ROS) -scavenging and robust osteogenic bio-scaffold (denoted "FPBS") for in situ bone defect restoration under oxidative stress microenvironment. Initially, fullerol nanoparticles were attached to the surface of the bredigite scaffold via covalently inter-crosslinking with PDA. Upon injury, extracellular ROS capturing triggered the oxidative degradation of PDA, releasing fullerol nanoparticles to enter into cells for further intracellular ROS scavenging. In vitro, FPBS had good biocompatibility and excellent antioxidative capability. Furthermore, FPBS promoted the osteogenesis of stem cells with significant elevation of osteogenic markers. Finally, in vivo implantation of FPBS remarkably enhanced new bone formation in a rat critical calvarial defect model. Overall, with amelioration of the ROS microenvironment of injured tissue and enhancement of osteogenic differentiation of stem cells simultaneously, FPBS may hold great potential towards bone defect repair.

Reactive oxygen-scavenging polydopamine nanoparticle coated 3D nanofibrous scaffolds for improved osteogenesis: Toward an aging in vivo bone regeneration model

Tissue engineered scaffolds aimed at the repair of critical-sized bone defects lack adequate consideration for our aging society. Establishing an effective aged in vitro model that translates to animals is a significant unmet challenge. The in vivo aged environment is complex and highly nuanced, making it difficult to model in the context of bone repair. In this work, 3D nanofibrous scaffolds generated by the thermally-induced self-agglomeration (TISA) technique were functionalized with polydopamine nanoparticles (PD NPs) as a tool to improve drug binding capacity and scavenge reactive oxygen species (ROS), an excessive build-up that dampens the healing process in aged tissues. PD NPs were reduced by ascorbic acid (rPD) to further improve hydrogen peroxide (H2O2) scavenging capabilities, where we hypothesized that these functionalized scaffolds could rescue ROS-affected osteoblastic differentiation in vitro and improve new bone formation in an aged mouse model. rPDs demonstrated improved H2O2 scavenging activity compared to neat PD NPs, although both NP groups rescued the alkaline phosphatase activity (ALP) of MC3T3-E1 cells in presence of H2O2. Additionally, BMP2-induced osteogenic differentiation, both ALP and mineralization, was significantly improved in the presence of PD or rPD NPs on TISA scaffolds. While in vitro data showed favorable results aimed at improving osteogenic differentiation by PD or rPD NPs, in vivo studies did not note similar improvements in ectopic bone formation an aged model, suggesting that further nuance in material design is required to effectively translate to improved in vivo results in aged animal models.

Rod-Shaped Mesoporous Zinc-Containing Bioactive Glass Nanoparticles: Structural, Physico-Chemical, Antioxidant, and Immuno-Regulation Properties

Bioactive glass nanoparticles (BGNs) are applied widely in tissue regeneration. Varied micro/nanostructures and components of BGNs have been designed for different applications. In the present study, nanorod-shaped mesoporous zinc-containing bioactive glass nanoparticles (ZnRBGNs) were designed and developed to form the bioactive content of composite materials for hard/soft tissue repair and regeneration. The nanostructure and components of the ZnRBGNs were characterized, as were their cytocompatibility and radical-scavenging activity in the presence/absence of cells and their ability to modulate macrophage polarization. The ZnRBGNs possessed a uniform rod shape (length ≈ 500 nm; width ≈ 150 nm) with a mesoporous structure (diameter ≈ 2.4 nm). The leaching liquid of the nanorods at a concentration below 0.5 mg/mL resulted in no cytotoxicity. More significant improvements in the antioxidant and M1-polarization-inhibiting effects and the promotion of M2 polarization were found when culturing the cells with the ZnRBGNs compared to when culturing them with the RBGNs. The doping of the Zn element in RBGNs may lead to improved antioxidant and anti-inflammatory effects, which may be beneficial in tissue regeneration/repair.

Dual-functional Hydroxyapatite scaffolds for bone regeneration and precision drug delivery

Addressing infected bone defects remains a significant challenge in orthopedics, requiring effective infection control and bone defect repair. A promising therapeutic approach involves the development of dual-functional engineered biomaterials with drug delivery systems that combine antibacterial properties with osteogenesis promotion. The Hydroxyapatite composite scaffolds offer a one-stage treatment, eliminating the need for multiple surgeries and thereby streamlining the process and reducing treatment time. This review delves into the impaired bone repair mechanisms within pathogen-infected and inflamed microenvironments, providing a theoretical foundation for treating infectious bone defects. Additionally, it explores composite scaffolds made of antibacterial and osteogenic materials, along with advanced drug delivery systems that possess both antibacterial and bone-regenerative properties. By offering a comprehensive understanding of the microenvironment of infectious bone defects and innovative design strategies for dual-function scaffolds, this review presents significant advancements in treatment methods for infectious bone defects. Continued research and clinical validation are essential to refine these innovations, ensuring biocompatibility and safety, achieving controlled release and stability, and developing scalable manufacturing processes for widespread clinical application.

Application of Antioxidant Compounds in Bone Defect Repair

Bone defects caused by trauma, tumor resection, and infections are significant clinical challenges. Excessive reactive oxygen species (ROS) usually accumulate in the defect area, which may impair the function of cells involved in bone formation, posing a serious challenge for bone repair. Due to the potent ROS scavenging ability, as well as potential anti-inflammatory and immunomodulatory activities, antioxidants play an indispensable role in the maintenance and protection of bone health and have gained increasing attention in recent years. This narrative review aims to give an overview of the main research directions on the application of antioxidant compounds in bone defect repair over the past decade. In addition, the positive effects of various antioxidants and their biomaterial delivery systems in bone repair are summarized to provide new insights for exploring antioxidant-based strategies for bone defect repair.

A Factor-Free Hydrogel with ROS Scavenging and Responsive Degradation for Enhanced Diabetic Bone Healing

In view of the increased levels of reactive oxygen species (ROS) that disturb the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), the repair of diabetic bone defects remains a great challenge. Herein, a factor-free hydrogel is reported with ROS scavenging and responsive degradation properties for enhanced diabetic bone healing. These hydrogels contain ROS-cleavable thioketal (TK) linkers and ultraviolet (UV)-responsive norbornene (NB) groups conjugated with 8-arm PEG macromers, which are formed via UV crosslinking-mediated gelation. Upon reacting with high levels of ROS in the bone defect microenvironment, ROS-cleavable TK linkers are destroyed, allowing the responsive degradation of hydrogels, which promotes the migration of BMSCs. Moreover, ROS levels are reduced through hydrogel-mediated ROS scavenging to reverse BMSC differentiation from adipogenic to osteogenic phenotype. As such, a favorable microenvironment is created after simultaneous ROS scavenging and hydrogel degradation, leading to the effective repair of bone defects in diabetic mouse models, even without the addition of growth factors. Thus, this study presents a responsive hydrogel platform that regulates ROS scavenging and stromal degradation in bone engineering.

NOX4 and its association with myeloperoxidase and osteopontin in regulating endochondral ossification

IMPORTANCE

Endochondral ossification plays an important role in skeletal development. Recent studies have suggested a link between increased intracellular reactive oxygen species (ROS) and skeletal disorders. Moreover, previous studies have revealed that increasing the levels of myeloperoxidase (MPO) and osteopontin (OPN) while inhibiting NADPH oxidase 4 (NOX4) can enhance bone growth. This investigation provides further evidence by showing a direct link between NOX4 and MPO, OPN in bone function.

OBJECTIVE

This study investigates NOX4, an enzyme producing hydrogen peroxide, in endochondral ossification and bone remodeling. NOX4's role in osteoblast formation and osteogenic signaling pathways is explored.

METHODS

Using NOX4-deficient (NOX4-/-) and ovariectomized (OVX) mice, we identify NOX4's potential mediators in bone maturation.

RESULTS

NOX4-/- mice displayed significant differences in bone mass and structure. Compared to the normal Control and OVX groups. Hematoxylin and eosin staining showed NOX4-/- mice had the highest trabecular bone volume, while OVX had the lowest. Proteomic analysis revealed significantly elevated MPO and OPN levels in bone marrow-derived cells in NOX4-/- mice. Immunohistochemistry confirmed increased MPO, OPN, and collagen II (COLII) near the epiphyseal plate. Collagen and chondrogenesis analysis supported enhanced bone development in NOX4-/- mice.

CONCLUSIONS AND RELEVANCE

Our results emphasize NOX4's significance in bone morphology, mesenchymal stem cell proteomics, immunohistochemistry, collagen levels, and chondrogenesis. NOX4 deficiency enhances bone development and endochondral ossification, potentially through increased MPO, OPN, and COLII expression. These findings suggest therapeutic implications for skeletal disorders.

Multifunctional tannic acid-based nanocomposite methacrylated silk fibroin hydrogel with the ability to scavenge reactive oxygen species and reduce inflammation for bone regeneration

The microenvironment of bone defect site is vital for bone regeneration. Severe bone defect is often accompanied with severe inflammation and elevated generation of reactive oxygen species (ROS) during bone repair. In recent years, the unfriendly local microenvironment has been paid more and more attention. Some bioactive materials with the ability to regulate the microenvironment to promote bone regeneration urgently need to be developed. Here, we develop a multifunctional composite hydrogel composed of photo-responsive methacrylate silk fibroin (SFMA), laponite (LAP) nanocomposite and tannic acid (TA), aiming to endow hydrogel with antioxidant, anti-inflammatory and osteogenic induction ability. Characterization results confirmed that the SFMA-LAP@TA hydrogel could significantly improve the mechanical properties of hydrogel. The ROS-Scavenging ability of the hydrogel enabled bone marrow mesenchymal stem cells (BMSCs) to survive against H2O2-induced oxidative stress. In addition, the SFMA-LAP@TA hydrogel effectively decreased the expression of pro-inflammatory factors in RAW264.7. More importantly, the SFMA-LAP@TA hydrogel could enhance the expression of osteogenic markers of BMSCs under inflammatory condition and greatly promote new bone formation in a critical-sized cranial defect model. Above all, the multifunctional hydrogel could effectively promote bone regeneration in vitro and in vivo by scavenging ROS and reducing inflammation, providing a prospective strategy for bone regeneration.

Biomaterial design for regenerating aged bone: materiobiological advances and paradigmatic shifts

China's aging demographic poses a challenge for treating prevalent bone diseases impacting life quality. As bone regeneration capacity diminishes with age due to cellular dysfunction and inflammation, advanced biomaterials-based approaches offer hope for aged bone regeneration. This review synthesizes materiobiology principles, focusing on biomaterials that target specific biological functions to restore tissue integrity. It covers strategies for stem cell manipulation, regulation of the inflammatory microenvironment, blood vessel regeneration, intervention in bone anabolism and catabolism, and nerve regulation. The review also explores molecular and cellular mechanisms underlying aged bone regeneration and proposes a database-driven design process for future biomaterial development. These insights may also guide therapies for other age-related conditions, contributing to the pursuit of 'healthy aging'.

Biomimetic Therapeutics for Bone Regeneration: A Perspective on Antiaging Strategies

Advances in modern medicine and the significant reduction in infant mortality have steadily increased the population's lifespan. As more and more people in the world grow older, incidence of chronic, noncommunicable disease is anticipated to drastically increase. Recent studies have shown that improving the health of the aging population is anticipated to provide the most cost-effective and impactful improvement in quality of life during aging-driven disease. In bone, aging is tightly linked to increased risk of fracture, and markedly decreased regenerative potential, deeming it critical to develop therapeutics to improve aging-driven bone regeneration. Biomimetics offer a cost-effective method in regenerative therapeutics for bone, where there are numerous innovations improving outcomes in young models, but adapting biomimetics to aged models is still a challenge. Chronic inflammation, accumulation of reactive oxygen species, and cellular senescence are among three of the more unique challenges facing aging-induced defect repair. This review dissects many of the innovative biomimetic approaches research groups have taken to tackle these challenges, and discusses the further uncertainties that need to be addressed to push the field further. Through these research innovations, it can be noted that biomimetic therapeutics hold great potential for the future of aging-complicated defect repair.

Mesenchymal stem cells-derived extracellular vesicles protect against oxidative stress-induced xenogeneic biological root injury via adaptive regulation of the PI3K/Akt/NRF2 pathway

Xenogeneic extracellular matrices (xECM) for cell support have emerged as a potential strategy for addressing the scarcity of donor matrices for allotransplantation. However, the poor survival rate or failure of xECM-based organ transplantation is due to the negative impacts of high-level oxidative stress and inflammation on seed cell viability and stemness. Herein, we constructed xenogeneic bioengineered tooth roots (bio-roots) and used extracellular vesicles from human adipose-derived mesenchymal stem cells (hASC-EVs) to shield bio-roots from oxidative damage. Pretreatment with hASC-EVs reduced cell apoptosis, reactive oxygen species generation, mitochondrial changes, and DNA damage. Furthermore, hASC-EV treatment improved cell proliferation, antioxidant capacity, and odontogenic and osteogenic differentiation, while significantly suppressing oxidative damage by activating the phosphatidylinositol 3-kinase (PI3K)/Akt pathway and nuclear factor erythroid 2 (NFE2)-related factor 2 (NRF2) nuclear translocation via p62-associated Kelch-like ECH-associated protein 1 (KEAP1) degradation. Inhibition of PI3K/Akt and Nrf2 knockdown reduced antioxidant capacity, indicating that the PI3K/Akt/NRF2 pathway partly mediates these effects. In subcutaneous grafting experiments using Sprague-Dawley rats, hASC-EV administration significantly enhanced the antioxidant effect of the bio-root, improved the regeneration efficiency of periodontal ligament-like tissue, and maximized xenograft function. Conclusively, therefore, hASC-EVs have the potential to be used as an immune modulator and antioxidant for treating oxidative stress-induced bio-root resorption and degradation, which may be utilized for the generation and restoration of other intricate tissues and organs.

Bioinspired self-healing injectable nanocomposite hydrogels based on oxidized dextran and gelatin for growth-factor-free bone regeneration

Hydrogels with great biocompatibility, biodegradability, and mechanical properties, combined with osteoconductivity, osteoinductivity, and osteointegration as biomaterials for bone regeneration without adding exogenous growth factors and cells are highly appealing but challenging. Here, inspired by organic-inorganic analogues of natural bone tissue and the adhesion chemistry of mussels, nanocomposite hydrogels with self-healing, injectable, adhesive, antioxidant, and osteoinductive properties (termed GO-PHA-CPs) were constructed by Schiff base cross-linking between dopamine-modified gelatin (Gel-DA) and oxidized dextran (ODex). Furthermore, the hydrogel network was enhanced by the introduction of polydopamine-functionalized nanohydroxyapatite (PHA) by improving the interfacial compatibility between the rigid inorganic particles and the flexible hydrogel matrix. Bioactive cod peptides (CPs) with osteogenic activity from Atlantic cod were further incorporated into the nanocomposite hydrogel. As a result, the multicomponent nanocomposite hydrogel favored the adhesion and spreading of MC3T3-E1 cells. The increased ALP activity suggested that GO-PHA-CPs hydrogels contributed to the osteogenic differentiation of MC3T3-E1 cells. The suitability of GO-PHA-CPs hydrogels for enhancing bone regeneration in vivo was further confirmed by the rat femoral defect model. Our results indicate that the multifunctional GO-PHA-CPs nanocomposite hydrogels without growth factors are a promising and effective candidate material for bone regeneration.

The role of smart polymeric biomaterials in bone regeneration: a review

Addressing critical bone defects necessitates innovative solutions beyond traditional methods, which are constrained by issues such as immune rejection and donor scarcity. Smart polymeric biomaterials that respond to external stimuli have emerged as a promising alternative, fostering endogenous bone regeneration. Light-responsive polymers, employed in 3D-printed scaffolds and photothermal therapies, enhance antibacterial efficiency and bone repair. Thermo-responsive biomaterials show promise in controlled bioactive agent release, stimulating osteocyte differentiation and bone regeneration. Further, the integration of conductive elements into polymers improves electrical signal transmission, influencing cellular behavior positively. Innovations include advanced 3D-printed poly (l-lactic acid) scaffolds, polyurethane foam scaffolds promoting cell differentiation, and responsive polymeric biomaterials for osteogenic and antibacterial drug delivery. Other developments focus on enzyme-responsive and redox-responsive polymers, which offer potential for bone regeneration and combat infection. Biomaterials responsive to mechanical, magnetic, and acoustic stimuli also show potential in bone regeneration, including mechanically-responsive polymers, magnetic-responsive biomaterials with superparamagnetic iron oxide nanoparticles, and acoustic-responsive biomaterials. In conclusion, smart biopolymers are reshaping scaffold design and bone regeneration strategies. However, understanding their advantages and limitations is vital, indicating the need for continued exploratory research.

Engineering Antioxidant Surfaces for Titanium-Based Metallic Biomaterials

Prolonged inflammation induced by orthopedic metallic implants can critically affect the success rates, which can even lead to aseptic loosening and consequent implant failure. In the case of adverse clinical conditions involving osteoporosis, orthopedic trauma and implant corrosion-wear in peri-implant region, the reactive oxygen species (ROS) activity is enhanced which leads to increased oxidative stress. Metallic implant materials (such as titanium and its alloys) can induce increased amount of ROS, thereby critically influencing the healing process. This will consequently affect the bone remodeling process and increase healing time. The current review explores the ROS generation aspects associated with Ti-based metallic biomaterials and the various surface modification strategies developed specifically to improve antioxidant aspects of Ti surfaces. The initial part of this review explores the ROS generation associated with Ti implant materials and the associated ROS metabolism resulting in the formation of superoxide anion, hydroxyl radical and hydrogen peroxide radicals. This is followed by a comprehensive overview of various organic and inorganic coatings/materials for effective antioxidant surfaces and outlook in this research direction. Overall, this review highlights the critical need to consider the aspects of ROS generation as well as oxidative stress while designing an implant material and its effective surface engineering.

Multifunctional dendrimer@nanoceria engineered GelMA hydrogel accelerates bone regeneration through orchestrated cellular responses

Bone defects in patients entail the microenvironment that needs to boost the functions of stem cells (e.g., proliferation, migration, and differentiation) while alleviating severe inflammation induced by high oxidative stress. Biomaterials can help to shift the microenvironment by regulating these multiple events. Here we report multifunctional composite hydrogels composed of photo-responsive Gelatin Methacryloyl (GelMA) and dendrimer (G3)-functionalized nanoceria (G3@nCe). Incorporation of G3@nCe into GelMA could enhance the mechanical properties of hydrogels and their enzymatic ability to clear reactive oxygen species (ROS). The G3@nCe/GelMA hydrogels supported the focal adhesion of mesenchymal stem cells (MSCs) and further increased their proliferation and migration ability (vs. pristine GelMA and nCe/GelMA). Moreover, the osteogenic differentiation of MSCs was significantly stimulated upon the G3@nCe/GelMA hydrogels. Importantly, the capacity of G3@nCe/GelMA hydrogels to scavenge extracellular ROS enabled MSCs to survive against H₂O₂-induced high oxidative stress. Transcriptome analysis by RNA sequencing identified the genes upregulated and the signalling pathways activated by G3@nCe/GelMA that are associated with cell growth, migration, osteogenesis, and ROS-metabolic process. When implanted subcutaneously, the hydrogels exhibited excellent tissue integration with a sign of material degradation while the inflammatory response was minimal. Furthermore, G3@nCe/GelMA hydrogels demonstrated effective bone regeneration capacity in a rat critical-sized bone defect model, possibly due to an orchestrated capacity of enhancing cell proliferation, motility and osteogenesis while alleviating oxidative stress.

Ebselen restores peri-implantitis-induced osteogenic inhibition via suppressing BMSCs ferroptosis

It is hard to reconstruct bone defects in peri-implantitis due to osteogenesis inhibited by excessive ROS. Ferroptosis, a recently identified regulated cell death characterized by iron- and reactive oxygen species- (ROS-) dependent lipid peroxidation, provides us with a new explanation. Our study aims to explore whether ferroptosis is involved in peri-implantitis-inhibited osteogenesis and confirm ebselen, an antioxidant with glutathione peroxidase (GPx)-like activity, could inhibit ferroptosis and promote osteogenesis in peri-implantitis. In this study, we used LPS to mimic the microenvironment of peri-implantitis. The osteogenic differentiation of bone-marrow-derived mesenchymal stem cells (BMSCs) was assessed by alkaline phosphatase (ALP), Alizarin Red S, and mRNA and protein expression of osteogenic-related markers. Ferroptosis index analysis included iron metabolism, ROS production, lipid peroxidation and mitochondrial morphological changes. Iron overload, reduced antioxidant capability, excessive ROS, lipid peroxidation and the characteristic mitochondrial morphological changes of ferroptosis were observed in LPS-treated BMSCs, and adding Ferrostatin-1 (Fer-1) restored the inhibitory effect of ferroptosis on osteogenic differentiation of BMSCs. Furthermore, ebselen ameliorated LPS-induced ferroptosis and osteogenic inhibition, which was reversed by erastin. Our results demonstrated that ferroptosis is involved in osteogenic inhibition in peri-implantitis and ebselen could attenuate osteogenic dysfunction of BMSCs via inhibiting ferroptosis.

Enhanced osteogenic differentiation and mineralization of human dental pulp stem cells using Prunus amygdalus amara (bitter almond) incorporated nanofibrous scaffold

Polyphenol extracts derived from plants are expected to have enhanced osteoblast proliferation and differentiation ability, which has gained much attention in tissue engineering applications. Herein, for the first time, we investigate the effects of Prunus amygdalus amara (bitter almond) (BA) extract loaded on poly (ε-caprolactone) (PCL)/gelatin (Gt) nanofibrous scaffolds on the osteoblast differentiation of human dental pulp stem cells (DPSCs). In this regard, BA (0, 5, 10, and 15% wt)-loaded PCL/Gt nanofibrous scaffolds were prepared by electrospinning with fiber diameters in the range of around 237-276 nm. Morphology, composition, porosity, hydrophilicity, and mechanical properties of the scaffolds were examined by FESEM, ATR-FTIR spectroscopy, BET, contact angle, and tensile tests, respectively. It was found that the addition of BA improved the tensile strength (up to 6.1 times), Young's modulus (up to 3 times), and strain at break (up to 3.2 times) compared to the neat PCL/Gt nanofibers. Evaluations of cell attachment, spreading, and proliferation were done by FESEM observation and MTT assay. Cytocompatibility studies support the biocompatible nature of BA loaded PCL/Gt scaffolds and free BA by demonstrating cell viability of more than 100% in all groups. The results of alkaline phosphatase activity and Alizarin Red assay revealed that osteogenic activity levels of BA loaded PCL/Gt scaffolds and free BA were significantly increased compared to the control group (p < 0.05, p < 0.01, p < 0.001). QRT-PCR results demonstrated that BA loaded PCL/Gt scaffolds and free BA led to a significant increase in osteoblast differentiation of DPSCs through the upregulation of osteogenic related genes compared to the control group (p < 0.05). Based on results, incorporation of BA extract in PCL/Gt scaffolds exhibited synergistic effects on the adhesion, proliferation, and osteogenesis differentiation of hDPSCs and was therefore assumed to be a favorable scaffold for bone tissue engineering applications.

Polyphenolic-modified cellulose acetate membrane for bone regeneration through immunomodulation

To enhance the bioactivity of cellulosic derivatives has become an important strategy to promote their value for clinical applications. Herein, protocatechualdehyde (PCA), a polyphenolic molecule, was used to modify a cellulose acetate (CA) membrane by combining with metal ions to confer an immunomodulatory activity. The PCA-modified CA membrane has shown a significant radical scavenging activity, thereby suppressed the inflammatory response and created a favorable immune microenvironment for osteogenesis and mineralization. Moreover, addition of metal ions could further stimulate the osteogenic differentiation of stem cells and accelerate bone regeneration both in vitro and in vivo. This study may provide a strategy to promote the immunomodulatory activity of cellulose-based biomaterials for bone regeneration.

Mesoporous TiO2 Coatings Regulate ZnO Nanoparticle Loading and Zn2+ Release on Titanium Dental Implants for Sustained Osteogenic and Antibacterial Activity

Two major issues are currently hindering the clinical practice of titanium dental implants for the lack of biological activities: immediate/early loading risks and peri-implantitis. To solve these issues, it is urgent to develop multifunctional implants modified with effective osteogenic and antibacterial properties. Zinc oxide nanoparticles (ZnO NPs) possess superior antibacterial activity; however, they can rapidly release Zn²⁺, causing cytotoxicity. In this study, a potential dental implant modification was creatively developed as ZnO nanoparticle-loaded mesoporous TiO₂ coatings (nZnO/MTC-Ti) via the evaporation-induced self-assembly method (EISA) and one-step spin coating. The mesoporous TiO₂ coatings (MTCs) regulated the synthesis and loading of ZnO NPs inside the nanosized pores. The synergistic effects of MTC and ZnO NPs on nZnO/MTC-Ti not only controlled the long-term steady-state release of Zn²⁺ but also optimized the charge distribution on the surface. Therefore, the cytotoxicity of ZnO NPs was resolved without triggering excessive reactive oxygen species (ROS). The increased extracellular Zn²⁺ further promoted a favorable intracellular zinc ion microenvironment through the modulation of zinc transporters (ZIP1 and ZnT1). Owing to that, the adhesion, proliferation, and osteogenic activity of bone mesenchymal stem cells (BMSCs) were improved. Additionally, nZnO/MTC-Ti inhibited the proliferation of oral pathogens (Pg and Aa) by inducing bacterial ROS production. For in vivo experiments, different implants were implanted into the alveolar fossa of Sprague-Dawley rats immediately after tooth extraction. The nZnO/MTC-Ti implants were found to possess a higher capability for enhancing bone regeneration, antibiosis, and osseointegration in vivo. These findings suggested the outstanding performance of nZnO/MTC-Ti implants in accelerating osseointegration and inhibiting bacterial infection, indicating a huge potential for solving immediate/early loading risks and peri-implantitis of dental implants.

Insight into the effect of biomaterials on osteogenic differentiation of mesenchymal stem cells: A review from a mitochondrial perspective

Bone damage may be triggered by a variety of factors, and the damaged area often requires a bone graft. Bone tissue engineering can serve as an alternative strategy for repairing large bone defects. Mesenchymal stem cells (MSCs), the progenitor cells of connective tissue, have become an important tool for tissue engineering due to their ability to differentiate into a variety of cell types. The precise regulation of the growth and differentiation of the stem cells used for bone regeneration significantly affects the efficiency of this type of tissue engineering. During the process of osteogenic induction, the dynamics and function of localized mitochondria are altered. These changes may also alter the microenvironment of the therapeutic stem cells and result in mitochondria transfer. Mitochondrial regulation not only affects the induction/rate of differentiation, but also influences its direction, determining the final identity of the differentiated cell. To date, bone tissue engineering research has mainly focused on the influence of biomaterials on phenotype and nuclear genotype, with few studies investigating the role of mitochondria. In this review, we provide a comprehensive summary of researches into the role of mitochondria in MSCs differentiation and critical analysis regarding smart biomaterials that are able to "programme" mitochondria modulation was proposed. STATEMENT OF SIGNIFICANCE: : • This review proposed the precise regulation of the growth and differentiation of the stem cells used to seed bone regeneration. • This review addressed the dynamics and function of localized mitochondria during the process of osteogenic induction and the effect of mitochondria on the microenvironment of stem cells. • This review summarized biomaterials which affect the induction/rate of differentiation, but also influences its direction, determining the final identity of the differentiated cell through the regulation of mitochondria.

Multiscale design of stiffening and ROS scavenging hydrogels for the augmentation of mandibular bone regeneration

Although biomimetic hydrogels play an essential role in guiding bone remodeling, reconstructing large bone defects is still a significant challenge since bioinspired gels often lack osteoconductive capacity, robust mechanical properties and suitable antioxidant ability for bone regeneration. To address these challenges, we first engineered molecular design of hydrogels (gelatin/polyethylene glycol diacrylate/2-(dimethylamino)ethyl methacrylate, GPEGD), where their mechanical properties were significantly enhanced via introducing trace amounts of additives (0.5 wt%). The novel hybrid hydrogels show high compressive strength (>700 kPa), stiff modulus (>170 kPa) and strong ROS-scavenging ability. Furthermore, to endow the GPEGD hydrogels excellent osteoinductions, novel biocompatible, antioxidant and BMP-2 loaded polydopamine/heparin nanoparticles (BPDAH) were developed for functionalization of the GPEGD gels (BPDAH-GPEGD). In vitro results indicate that the antioxidant BPDAH-GPEGD is able to deplete elevated ROS levels to protect cells viability against ROS damage. More importantly, the BPDAH-GPEGD hydrogels have good biocompatibility and promote the osteo differentiation of preosteoblasts and bone regenerations. At 4 and 8 weeks after implantation of the hydrogels in a mandibular bone defect, Micro-computed tomography and histology results show greater bone volume and enhancements in the quality and rate of bone regeneration in the BPDAH-GPEGD hydrogels. Thus, the multiscale design of stiffening and ROS scavenging hydrogels could serve as a promising material for bone regeneration applications.

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Trace additives of DMAEMA markedly enhanced the mechanical performances of the gelatin-based hydrogels through molecular induced multiple crosslinking structures.

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Molecular design strategy combined with bioactive nanocomposites have a synergistically effects on promoting ROS scavenging ability and osteoactivity of the biomimetic hydrogels.

Immune response differences in degradable and non-degradable alloy implants

Alloy based implants have made a great impact in the clinic and in preclinical research. Immune responses are one of the major causes of failure of these implants in the clinic. Although the immune responses toward non-degradable alloy implants are well documented, there is a poor understanding of the immune responses against degradable alloy implants. Recently, there have been several reports suggesting that degradable implants may develop substantial immune responses. This phenomenon needs to be further studied in detail to make the case for the degradable implants to be utilized in clinics. Herein, we review these new recent reports suggesting the role of innate and potentially adaptive immune cells in inducing immune responses against degradable implants. First, we discussed immune responses to allergen components of non-degradable implants to give a better overview on differences in the immune response between non-degradable and degradable implants. Furthermore, we also provide potential areas of research that can be undertaken that may shed light on the local and global immune responses that are generated in response to degradable implants.

The Application of Black Phosphorus Nanomaterials in Bone Tissue Engineering

Recently, research on and the application of nanomaterials such as graphene, carbon nanotubes, and metal-organic frameworks has become increasingly popular in tissue engineering. In 2014, a two-dimensional sheet of black phosphorus (BP) was isolated from massive BP crystals. Since then, BP has attracted significant attention as an emerging nanomaterial. BP possesses many advantages such as light responsiveness, electrical conductivity, degradability, and good biocompatibility. Thus, it has broad prospects in biomedical applications. Moreover, BP is composed of phosphorus, which is a key bone tissue component with good biocompatibility and osteogenic repair ability. Thereby, BP exhibits excellent advantages for application in bone tissue engineering. In this review, the structure and the physical and chemical properties of BP are described. In addition, the current applications of BP in bone tissue engineering are reviewed to aid the future research and application of BP.

The potential of oxygen and nitrogen species-regulating drug delivery systems in medicine

The focus of this review is to present most significant advances in biomaterials used for control of reactive oxygen/nitrogen species (ROS/RNS, RONS) in medicine. A summary of the main pathways of ROS production and the main pathways of RNS production are shown herein. Although the physiological and pathological roles of RONS have been known for at least 2decades, the potential of their control in management of disease went unappreciated. Recently, advances in the field of biochemical engineering and materials science have allowed for development of RONS-responsive biomaterials for biomedical applications, which aim to control and change levels of reactive species in tissue microenvironments. These materials utilize polymers, inorganic nanoparticles (NPs), or organic-inorganic hybrids. Thus, biomaterials like hydrogels have been developed to promote tissue regeneration by actively scavenging and reducing RONS levels. Their promising utility comes from thermo- and RONS-sensitivity, stability as a delivery-medium, ease for incorporation into other materials and facility for injection. Their particular attractiveness is attributed to drug release realized in targeted tissues and cells with elevated RONS levels, which leads to enhanced treatment outcomes and reduced adverse effects. The mechanism of their action depends on the functional groups employed and their response to oxidation, and may be based on solubility changes or cleavage of chemical bonds. When talking about antioxidants, one should also mention oxidative stress, which we call the imbalance between antioxidants and reactive oxygen species, which occurs due to a deficiency of endogenous antioxidants and a low supply of exogenous antioxidants. This study is a review of articles in English from the databases PubMed and Web of Science retrieved by applying the search terms “Oxygen Species, Nitrogen Species and biomaterials” from 1996 to 2021.

The Importance of Antioxidant Biomaterials in Human Health and Technological Innovation: A Review

Biomaterials come from natural sources such as animals, plants, fungi, algae, and bacteria, composed mainly of protein, lipid, and carbohydrate molecules. The great diversity of biomaterials makes these compounds promising for developing new products for technological applications. In this sense, antioxidant biomaterials have been developed to exert biological and active functions in the human body and industrial formulations. Furthermore, antioxidant biomaterials come from natural sources, whose components can inhibit reactive oxygen species (ROS). Thus, these materials incorporated with antioxidants, mainly from plant sources, have important effects, such as anti-inflammatory, wound healing, antitumor, and anti-aging, in addition to increasing the shelf-life of products. Aiming at the importance of antioxidant biomaterials in different technological segments as biodegradable, economic, and promising sources, this review presents the main available biomaterials, antioxidant sources, and assigned biological activities. In addition, potential applications in the biomedical and industrial fields are described with a focus on innovative publications found in the literature in the last five years.

Inflammation-mediated matrix remodeling of extracellular matrix-mimicking biomaterials in tissue engineering and regenerative medicine

Extracellular matrix (ECM)-mimicking biomaterials are considered effective tissue-engineered scaffolds for regenerative medicine because of their biocompatibility, biodegradability, and bioactivity. ECM-mimicking biomaterials preserve natural microstructures and matrix-related bioactive components and undergo continuous matrix remodeling upon transplantation. The interaction between host immune cells and transplanted ECM-mimicking biomaterials has attracted considerable attention in recent years. Transplantation of biomaterials may initiate injuries and early pro-inflammation reactions characterized by infiltration of neutrophils and M1 macrophages. Pro-inflammation reactions may lead to degradation of the transplanted biomaterial and drive the matrix into a fetal-like state. ECM degradation leads to the release of matrix-related bioactive components that act as signals for cell migration, proliferation, and differentiation. In late stages, pro-inflammatory cells fade away, and anti-inflammatory cells emerge, which involves macrophage polarization to the M2 phenotype and leukocyte activation to T helper 2 (Th2) cells. These anti-inflammatory cells interact with each other to facilitate matrix deposition and tissue reconstruction. Deposited ECM molecules serve as vital components of the mature tissue and influence tissue homeostasis. However, dysregulation of matrix remodeling results in several pathological conditions, such as aggressive inflammation, difficult healing, and non-functional fibrosis. In this review, we summarize the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. STATEMENT OF SIGNIFICANCE: Extracellular matrix (ECM)-mimicking biomaterials are effectively used as scaffolds in tissue engineering and regenerative medicine. However, dysregulation of matrix remodeling can cause various pathological conditions. Here, the review describes the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. We believe that understanding host immune responses to matrix remodeling of transplanted biomaterials is important for directing effective tissue regeneration of ECM-mimicking biomaterials. Considering the close relationship between immune response and matrix remodeling results, we highlight the need for studies of the effects of clinical characteristics on matrix remodeling of transplanted biomaterials.

Strontium Functionalized in Biomaterials for Bone Tissue Engineering: A Prominent Role in Osteoimmunomodulation

With the development of bone tissue engineering bio-scaffold materials by adding metallic ions to improve bone healing have been extensively explored in the past decades. Strontium a non-radioactive element, as an essential osteophilic trace element for the human body, has received widespread attention in the medical field due to its superior biological properties of inhibiting bone resorption and promoting osteogenesis. As the concept of osteoimmunology developed, the design of orthopedic biomaterials has gradually shifted from “immune-friendly” to “immunomodulatory” with the aim of promoting bone healing by modulating the immune microenvironment through implanted biomaterials. The process of bone healing can be regarded as an immune-induced procedure in which immune cells can target the effector cells such as macrophages, neutrophils, osteocytes, and osteoprogenitor cells through paracrine mechanisms, affecting pathological alveolar bone resorption and physiological bone regeneration. As a kind of crucial immune cell, macrophages play a critical role in the early period of wound repair and host defense after biomaterial implantation. Despite Sr-doped biomaterials being increasingly investigated, how extracellular Sr²⁺ guides the organism toward favorable osteogenesis by modulating macrophages in the bone tissue microenvironment has rarely been studied. This review focuses on recent knowledge that the trace element Sr regulates bone regeneration mechanisms through the regulation of macrophage polarization, which is significant for the future development of Sr-doped bone repair materials. We will also summarize the primary mechanism of Sr²⁺ in bone, including calcium-sensing receptor (CaSR) and osteogenesis-related signaling pathways.

Superoxide Dismutase and Glutathione Reductase as Indicators of Oxidative Stress Levels May Relate to Geriatric Hip Fractures' Survival and Walking Ability: A Propensity Score Matching Study

Background

Oxidative stress status may affect bone metabolism and regeneration. However, few studies reported whether oxidative stress could impact the outcomes of hip fractures. This study aimed to explore if superoxide dismutase and glutathione reductase, the critical antioxidant enzymes, correlated with the prognosis of hip fractures.

Methods

Patients with hip fractures were extracted from our database, and those who met the inclusion criteria were analyzed. Propensity score matching was used to reduce the influence of confounding factors, and ROC curves based on matched populations were created to determine the optimal cutoff points of SOD and GR. Then, outcomes between SOD or GR and outcomes of hip fractures were compared.

Results

Out of 301 patients enrolled in this study, 50 patients died within one year. After a 1:1 PSM, the patients with less than 1-year survival had significantly lower SOD (p = 0.026) and GR (p = 0.021) than those who were still alive at one year. Logistics analysis showed that low SOD and low GR may be independent risk factors for 6-month survival, 1-year survival, 6-month free walking ability, and 1-year free walking ability.

Conclusion

SOD and GR may be the independent risk factors for survival and walking abilities of hip fractures.

PgC3Mg metal-organic cages functionalized hydrogels with enhanced bioactive and ROS scavenging capabilities for accelerated bone regeneration

The repair of large bone defects is an urgent problem in the clinic. Note that the disruption of redox homeostasis around bone defect sites might hinder the new bone reconstruction. The rational design of hydrogels for bone regeneration still faces the challenges of insufficient antioxidant capability and weak osteogenesis performance. Here, motivated by the versatile therapeutic functions of metal-organic cages, magnesium-seamed C-propylpyrogallol[4]arene (PgC₃Mg) functionalized biodegradable and porous gelatin methacrylate (GelMA) hydrogels are constructed. The novel metal-organic cages endow hydrogels with highly bioactive characteristics and strong reactive oxygen species (ROS)-scavenging ability owing to the simultaneous release of bioactive Mg²⁺ ions and antioxidant phenolic hydroxyl-rich moieties. The in vitro results reveal that the PgC₃Mg modified biocompatible hydrogels show higher expression of osteo-related genes and significantly eliminate the intracellular ROS levels of bone marrow-derived mesenchymal stem cells (BMSCs) against oxidative damage. Meanwhile, the bioactive and ROS scavenging hydrogels can accelerate bone regeneration in large cranial defects. Overall, this study may provide new insights into the designing of regenerative bone grafts with simultaneously enhanced osteogenic and antioxidant capabilities.

Osteogenic Effect of Fisetin Doping in Bioactive Glass/Poly(caprolactone) Hybrid Scaffolds

Treating large bone defects or fragile patients may require enhancing the bone regeneration rate to overcome a weak contribution from the body. This work investigates the osteogenic potential of nutrient fisetin, a flavonoid found in fruits and vegetables, as a doping agent inside the structure of a SiO₂-CaO bioactive glass-poly(caprolactone) (BG-PCL) hybrid scaffold. Embedded in the full mass of the BG-PCL hybrid during one-pot synthesis, we demonstrate fisetin to be delivered sustainably; the release follows a first-order kinetics with active fisetin concentration being delivered for more than 1 month (36 days). The biological effect of BG-PCL-fisetin-doped scaffolds (BG-PCL-Fis) has been highlighted by in vitro and in vivo studies. A positive impact is demonstrated on the adhesion and the differentiation of rat primary osteoblasts, without an adverse cytotoxic effect. Implantation in critical-size mouse calvaria defects shows bone remodeling characteristics and remarkable enhancement of bone regeneration for fisetin-doped scaffolds, with the regenerated bone volume being twofold that of nondoped scaffolds and fourfold that of a commercial trabecular bovine bone substitute. Such highly bioactive materials could stand as competitive alternative strategies involving biomaterials loaded with growth factors, the use of the latter being the subject of growing concerns.

Application Progress of Modified Chitosan and Its Composite Biomaterials for Bone Tissue Engineering

In recent years, bone tissue engineering (BTE), as a multidisciplinary field, has shown considerable promise in replacing traditional treatment modalities (i.e., autografts, allografts, and xenografts). Since bone is such a complex and dynamic structure, the construction of bone tissue composite materials has become an attractive strategy to guide bone growth and regeneration. Chitosan and its derivatives have been promising vehicles for BTE owing to their unique physical and chemical properties. With intrinsic physicochemical characteristics and closeness to the extracellular matrix of bones, chitosan-based composite scaffolds have been proved to be a promising candidate for providing successful bone regeneration and defect repair capacity. Advances in chitosan-based scaffolds for BTE have produced efficient and efficacious bio-properties via material structural design and different modifications. Efforts have been put into the modification of chitosan to overcome its limitations, including insolubility in water, faster depolymerization in the body, and blood incompatibility. Herein, we discuss the various modification methods of chitosan that expand its fields of application, which would pave the way for future applied research in biomedical innovation and regenerative medicine.

Surface-Engineered Hybrid Gelatin Methacryloyl with Nanoceria as Reactive Oxygen Species Responsive Matrixes for Bone Therapeutics

Designing various transplantable biomaterials, especially nanoscale matrixes for bone regeneration, involves precise tuning of topographical features. The cellular fate on such engineered surfaces is highly influenced by many factors imparted by the surface modification (hydrophilicity, stiffness, porosity, roughness, ROS responsiveness). Herein, hybrid matrixes of gelatin methacryloyl (GelMA) decorated with uniform layers of nanoceria (nCe), called Ce@GelMA, were developed without direct incorporation of nCe into the scaffolds. The fabrication involves a simple base-mediated in situ deposition in which uniform nCe coatings were first made on GelMA hydrogels and then nCe layered GelMA scaffolds were made by cryodesiccation. In this hybrid platform, degradable GelMA biopolymer provides the porous microstructure and nCe provides the nanoscaled biointerface. The surface morphology and elemental composition of the matrixes analyzed by field emission scanning electron microscopy (FE-SEM) and energy-dispersive spectroscopy (EDS) show uniform nCe distribution. The surface nanoroughness and chemistry of the matrixes were also characterized using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The presence of nCe on GelMA enhanced its mechanical properties as confirmed by compressive modulus analysis. Substantial bonelike nanoscale hydroxyapatite formation was observed on scaffolds after simulated body fluid (SBF) immersion, which was confirmed by SEM, X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. Moreover, the developed scaffolds could also be used as an antioxidant matrix owing to the reactive oxygen species (ROS) scavenging property of nCe as assessed by 3,3',5,5'-tetramethylbenzidine (TMB) assay. The enhanced proliferation and viability of rat bone marrow mesenchymal stem cells (rMSCs) on the scaffold surface after 3 days of culture ensures the biocompatibility of the proposed material. Considering all, it is proposed that the micro/nanoscaled matrix could mimic the composition and function of hard tissues and could be utilized as degradable scaffolds in engineering bones.

Understanding Reactive Oxygen Species in Bone Regeneration: A Glance at Potential Therapeutics and Bioengineering Applications

Although the complex mechanism by which skeletal tissue heals has been well described, the role of reactive oxygen species (ROS) in skeletal tissue regeneration is less understood. It has been widely recognized that a high level of ROS is cytotoxic and inhibits normal cellular processes. However, with more recent discoveries, it is evident that ROS also play an important, positive role in skeletal tissue repair, specifically fracture healing. Thus, dampening ROS levels can potentially inhibit normal healing. On the same note, pathologically high levels of ROS cause a sharp decline in osteogenesis and promote nonunion in fracture repair. This delicate balance complicates the efforts of therapeutic and engineering approaches that aim to modulate ROS for improved tissue healing. The physiologic role of ROS is dependent on a multitude of factors, and it is important for future efforts to consider these complexities. This review first discusses how ROS influences vital signaling pathways involved in the fracture healing response, including how they affect angiogenesis and osteogenic differentiation. The latter half glances at the current approaches to control ROS for improved skeletal tissue healing, including medicinal approaches, cellular engineering, and enhanced tissue scaffolds. This review aims to provide a nuanced view of the effects of ROS on bone fracture healing which will inspire novel techniques to optimize the redox environment for skeletal tissue regeneration.